The present invention is directed to an electronically commutated polyphase synchronous machine as recited in the preamble of claim 1.
In a known three-phase synchronous motor, also called EC motor (German Patent 40 40 926 C1), the stator winding is designed as a star connection whose star point is connected to the positive potential of the direct voltage system. The circuit device for operating the synchronous motor has three power transistors designed as MOSFETs (metal-oxide semiconductor field-effect transistors) which are connected in series with a winding phase of the stator winding, the drains being connected to the associated winding phase and the sources being connected to the lower potential, i.e., the ground potential of the direct voltage system, via a common resistor. The switching signals, generated by the commutation device, are applied to the gates of the power MOSFETs forming the difference with a reference voltage picked off at the resistor. For the rotor position query, three position sensors are provided which generate output signals according to the angular position of the rotor, the output signals being electrically converted in a gate circuit into a three-phase signal without overlap, with a pitch of 120xc2x0. The three-phase signal is supplied to the commutation device which generates the above-mentioned switching signals for the power transistors, the signals being composed of a sequence of periodic square-wave pulses.
The electronically commutated polyphase synchronous machine according to the present invention having the features as recited in claim 1 has the advantage of a sensorless detection of the angular position of the rotor, which is very attractive from a cost standpoint. The analysis of the voltage, induced in the at least one auxiliary winding, for obtaining information concerning the angular position of the rotor not requiring a complex circuitry is possible in a simple way.
The insertion of only one auxiliary winding into the stator, and its assignment to a winding phase, delivers only one rotor position information per electric revolution of the synchronous machine, which is frequently sufficient for drives having low dynamics requirements. For a higher dynamics requirement an auxiliary winding is added to each winding phase, so that the switching signals for each winding phase of the stator winding are synchronized with the angular position of the rotor, thus, in a three-phase synchronous machine synchronization takes place electrically during each angular displacement of the rotor by 120xc2x0.
The measures listed in the subsequent claims make advantageous refinements of and improvements on the synchronous machine mentioned in claim 1 possible.
According to an advantageous embodiment of the present invention, each auxiliary winding is assigned a zero crossing detector which detects when the voltage induced in each auxiliary winding exceeds or drops below a reference potential and outputs it as a rotor angular position signal. The reference potential is preferably ground, but it may also be adjusted in a defined manner using a reference voltage source.
According to an advantageous embodiment of the present invention, each auxiliary winding is manufactured from a winding wire having a small cross section. Thus, the auxiliary windings require only little winding space in the stator. The small wire cross section or wire diameter is possible since only minimum currents flow in the auxiliary windings.
According to an advantageous embodiment of the present invention, the auxiliary windings are wound with a number of turns as large as possible, resulting in an increased amplitude of the induced voltages and a better analysis of the same.